HowTo WLAN Repeater CrossBand with MikroTik RouterOS


Simplifed HowTo Guide, mostly for private networks at home. Enterprises might/should use enterprise wireless security settings, enterprise wifi site survey etc. Please Note: As always: No guarantee; Always backup your existing config before changing anything; Harden your setup (see below);

1. Intro

Howto expand your WiFi with two different wireless radios.

Example:
|Original AP| -------- 2.4Ghz Chan 1 SSID1 -------- |MikroTik AP|-------- 5 Ghz Chan 36 SSID1 --------

SSID1 extended with MikroTik AP on another band & channel

2.    HowTo Guide with MikroTik

HowTo Guide with MikroTik hAP2 (dual radio access point) in RouterOS v6.42.6 (stable)

You should have:
  • Your MikroTik dual radio access point available, powered on, have access to it 
  • Think about doing a firmware update to the latest stable firmware
  • Backup your existing RouterOS cfg
  • Information about your wifi you want to extend (SSID name, Pre-Shared-Key (PSK), on which band and channel it is broadcasted)

2.1. Connect to existing wireless network with radio1

2.1.1.       Access GUI & Login

2.1.2.       Select Wireless -> Security Profiles -> Add new:

2.1.3. SecurityProfile-Name

  • Enter a SecurityProfile-Name, for example: SecProf-yourSSIDname
  • Select the authentication type of your existing wifi
  • Enter the Pre-Shared-Key (PSK) of your existing wifi:

2.1.4. Wireless -> Scanner


2.1.5. Select wlan1 as interface and press start

2.1.6. Select your wireless signal which you want to extend

2.1.7. Press connect

 

2.1.8. Wireless\WiFi interfaces -> Select wlan1

2.1.9. Setup the first radio as „wireless client“

  • Set mode to „station pseudobridge 
  • Set band to the band of your existing wifi 
  • Set frequency to the channel of your existing wifi or use auto 
  • Use the security profile you created in step 2.1.2. and 2.1.3. with the correct psk:  

Tip: Try to not use 802.11b due to bad performance, if possible only use 802.11n (as in screenshot) or 11g & n

Press apply. The status should change to „connected to ess":

2.2. Extend your existing wireless network with radio2

2.2.1 Wireless\WiFi Interfaces -> Select wlan2

2.2.2. Setup the second radio as „wireless access point“

  • Set mode to „ap bridge 
  • Set band to the band of the extended wifi signal
  • Set frequency to the channel for the extended wifi signal (if possible a free channel) 
  • Use the same SSID name as your existing wifi 
  • Use the security profile you created in step 2. and 3. with the correct psk 
  • Set bridge mode to enabled

2.3. Connect both radios with each other using a bridge

2.3.1. Bridge\Bridge -> Add new

2.3.2. Enter a name for the bridge, for example WLAN-Bridge01:

Confirm with OK

2.3.3. Assign both wireless interfaces to bridge:

Bridge\Ports -> Select wlan1:

2.3.4. Set Bridge to your created Bridge (from step 13, for example WLAN-Bridge01):

2.3.5. Assign second wireless interfaces to bridge:

Bridge\Ports -> Select wlan2:

2.3.6. Set Bridge to your created Bridge (from step 13, for example WLAN-Bridge01):

2.3.7. Safe your MikroTik configuration

2.3.8. Test to connect to your extened WiFi

3. General WiFi-Tips

  • Do a wireless site survey (perfect heatmap with non-overlapping channels and keep it updated after wifi is alive and changes)
  • Use 20Mhz channels when there is a lot of noise in the air
  • Use strong wireless security (wpa2-enterprise or long wpa2-psks with aes-ccm)
  • Check for rogue access points (e.g. with access points with 3 radios)
  • Harden your MikroTik
  • Keep your wifi solutions up to date
  • Turn of old wireless standards as tkip, wep, wpa1, 802.11b
  • Use band steering & disconnected clients at a low signal strength to force them to roam

FortiGate Path MTU Discovery

FortiOS PMTU Cmd

FortiOS supports RFC 1191 "Path MTU Discovery IPv4" and RFC 1981 (PMTU IPv6), a technique for dynamically discovering the maximum transmission unit (MTU) of an arbitrary internet path.

It can be checked using the following command, which lists the routing cache:

diag ip rtcache list
 
Example output:

FGT51E3U00000000 # c v
FGT51E3U00000000
(vdom) # edit root
current vf=root:0


FGT51E3U00000000 (root) # diag ip rtcache list

family=02 tab=254 vf=0 type=01 tos=0 flag=00000200
1.2.3.4@0->192.168.117.15@18(LAN-HardwSwitch) gwy=192.168.1.1 prefsrc=0.0.0.0
ci: ref=0 lastused=199 expire=0 err=00000000 used=3 br=0 pmtu=1500

family=02 tab=254 vf=0 type=01 tos=0 flag=04000200
192.168.1.1@18(LAN-HardwSwitch)->194.1.2.3@4(wan1) gwy=192.168.0.1 prefsrc=192.168.1.254
ci: ref=1 lastused=159 expire=0 err=00000000 used=0 br=0 pmtu=1500

family=02 tab=254 vf=0 type=01 tos=0 flag=04000200
192.168.1.1@18(LAN-HardwSwitch)->
194.1.2.3@4(wan1) gwy=192.168.0.1 prefsrc=192.168.1.254
ci: ref=1 lastused=4 expire=0 err=00000000 used=0 br=0 pmtu=1500

family=02 tab=254 vf=0 type=01 tos=0 flag=00000200
148.0.0.1@0->192.168.1.1@18(LAN-HardwSwitch) gwy=0.0.0.0 prefsrc=0.0.0.0
ci: ref=0 lastused=239 expire=0 err=00000000 used=24 br=0 pmtu=1500

family=02 tab=254 vf=0 type=01 tos=0 flag=00000200
104.1.2.3@0->192.168.1.1@18(LAN-HardwSwitch) gwy=0.0.0.0 prefsrc=0.0.0.0
ci: ref=0 lastused=626 expire=0 err=00000000 used=3 br=0 pmtu=1500

family=02 tab=254 vf=0 type=01 tos=0 flag=00000200
192.168.1.1@0->104.2.3.4@4(wan1) gwy=192.168.0.1 prefsrc=0.0.0.0
ci: ref=0 lastused=441 expire=0 err=00000000 used=2 br=0 pmtu=1500
 

family=02 tab=254 vf=0 type=01 tos=0 flag=04000200
192.168.1.1@18(LAN-HardwSwitch)->170.1.2.3@4(wan1) gwy=192.168.0.1 prefsrc=192.168.1.254
ci: ref=4 lastused=14 expire=0 err=00000000 used=2 br=0 pmtu=1500


What is Path MTU Discovery? 

Wikipedia:
Path MTU Discovery (PMTUD) is a standardized technique in computer networking for determining the maximum transmission unit (MTU) size on the network path between two Internet Protocol (IP) hosts, usually with the goal of avoiding IP fragmentation. PMTUD was originally intended for routers in Internet Protocol Version 4 (IPv4).[1] However, all modern operating systems use it on endpoints. In IPv6, this function has been explicitly delegated to the end points of a communications session.

General hints:

  • Please do not mix up layer 2 ethernet frame size and layer 3 ip mtu paket size. If you want to use for example jumbo-frames you have to change both, the l2 ethernet frame size at your switches/network devices and l3 ip mtu size at you routers/firewall/network devices.
  • For testing MTU do not relay on checking if google is available or RDP-connections are working. Both and many more applications/services use techniques to overcome wrong frame-size/mtu-size implementations.
  • When having issues with packets over virtual tunnels like for example IPSec or when setting up new interfaces/links or when using dynamic routing protocols like OSPF or BGP, checking the mtu is always a good idea.

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